1. Field of the Invention
This invention relates to coning control in oil/gas wells and more particularly, to a dual completion method of controlling the coning of water into hydrocarbons such as oil and gas by perforating a common producing oil strata or formation in vertically-spaced relationship above and below the oil-water interface in the formation and producing both the oil and water in a controlled manner separately from the well.
One of the problems encountered in oil and gas production over the years is the production of salt water in the well, a circumstance which increases operating costs and decreases revenue in most operating circumstances. The increased operating cost under such conditions is due to several factors, among which are the requirement for larger tubing and/or more expensive artificial pumping systems to handle the increased volume caused by water production with the oil and or other hydrocarbons to separate the water from the oil at the surface. The increasing water/oil ratios in the well production fluid lead to decreased oil/gas production, lower revenues and lower ultimate recoveries, in most cases and the problem is particularly acute in fields that are known for high water cut production. Most of these sands have a very strong natural water drive and many oil reservoirs have an oil-water contact zone with the water column characterized by up to 10 to 90 percent of the height. This condition leads to bottom water coning that takes place very rapidly due to the clean nature of many of the sands. For example, these clean sands are typically characterized by one to four darcy permeability and have very high vertical to horizontal permeability ratios.
2. Description of the Prior Art
Among the parameters which affect water coning in vertical oil wells are the mobility ratio, oil zone thickness, ratio of gravity forces to viscous forces, well spacing, ratio of horizontal permeability to vertical permeability and well penetration and production rate. While some of these variables are technically virtually uncontrollable, it has been found that water coning may be successfully controlled according to the technique of this invention. Accordingly, the dual completion method of this invention is designed to increase the hydrocarbon productivity as well as the amount of hydrocarbon ultimately recovered from the well. Efforts to explore methods and apparatus for controlling these variables in effecting a successful dual completion technique include computer simulations and production projections based on these simulations. The dual completion method of this invention was implemented with the following objectives in mind:
1. To prevent or minimize the coning of water into oil at hydrocarbon production rates exceeding computer model simulations, utilizing the dual completion method of this invention.
2. To produce oil and/or gas for an extended period of time at a production rate in excess of past sustainable rates of production from surrounding wells.
3. To produce oil directly to the collection tank without any treatment to remove water.
4. To produce salt water directly to a disposal system without any treatment to remove hydrocarbons.
5. To determine water coning characteristics of the particular sand under consideration and the economical benefits of the method of this invention.
6. To measure and compare hydrocarbon contamination of water from the method of this invention and compare this hydrocarbon contamination with like contamination in conventional systems.
Another object of this invention is to provide a new and improved method of controlling coning in hydrocarbon-producing wells, which method includes the steps of drilling a well through a hydrocarbon-producing interval to a selected depth or reworking an existing well, perforating the producing interval above and below the hydrocarbon-water contact zone in the formation and producing both hydrocarbons and water from the spaced perforations in the well at a controlled rate. This technique facilitates production of hydrocarbons such as oil and water in a stable oil-water condition which maximizes the wells' profitability.